Included among the known 2-carboxyethyl- and carboxymethylphosphines and the alkali metal salts thereof are: tris(2-carboxyethyl)phosphine [Journal of General Chemistry of the USSR 46: 275 (1976).sup.(1) ] and bis(carboxymethyl)phenylphosphine, as well as the sodium and potassium salts thereof [Collect. Czechslov. Chem. Commun. 43: 57 (1978).sup.(2) ].
Such phosphines are used for flameproofing polymers (1) and for complexing metal ions (2). According to (1), tris(2-carboxyethyl)phosphine is obtained by heating the corresponding nitrile to 90.degree.-95.degree. C. with a strongly acidic ion exchanger, vacuum-filtering the ion exchanger and evaporating the resultant aqueous solution. According to (2), bis(carboxymethyl)phenylphosphine is produced by reacting the Reformatsky reagent BrZnCH.sub.2 COOC.sub.2 H.sub.5 with phenyldichlorophosphine, saponifying the thus-formed ester C.sub.6 H.sub.5 P(CH.sub.2 COOC.sub.2 H.sub.5).sub.2 with sodium hydroxide solution and treating the resultant sodium salt with 10% sulfuric acid. In both cases, the phosphinocarboxylic acid is only produced in moderate yields. Additionally, the mentioned synthesis for the production of bis(carboxymethyl)phenylphosphine is a multistage one and, consequently, is expensive.
These disadvantages are becoming increasingly significant since carboxyalkyl phosphines have gained increasing industrial importance. For example, it is known from DAS's [German Published Applications] 1,955,828 and 2,022,184 to utilize such compounds as ligands for transition metal catalysts in the hydroformulation of olefins. It is also known from DOS's [German Unexamined Laid-Open Applications] 2,053,758; 2,054,009; 2,054,083; 2,159,370; 2,234,734; 2,264,088; 2,341,472; 2,445,362; and 2,656,383 to employ tertiary organophosphorus compounds of the formula R".sub.2 P-(CH.sub.2).sub.n -COOM wherein n=1 or 2; M=H or an alkali metal; and R"=a monovalent organic residue of 1-20 carbon atoms, as nickel ligands in ethylene oligomerization.